Okay the story goes like this I filled up at a busy speedway station then went across the street to buffalo wild wings for some food. When I leave my truck runs fine for less than a mile before starting to miss and pop eventually bringing up a po300 code.

I drive back to the station ask if there has been any other reports of this and of course there has not been. But they give me some dry-gas and that did not help.

The truck will run evenly if no load is put on the engine, but if you try to go it starts missing badly and it has a pretty bad idle once fully warm. But it will start quickly.

So I ended up limping it home and just to be sure I filled a glass jar with gas from the tank and have let it set and still found no trace of water.

As far as parts go within the last 12 months I have replaced the following on the ignition system
- AC Delco Plugs
- Non-AC Delco Wires
- Cap and rotor non AC

I understand that these are very sensitive to AC delco parts but with roughly 10k on these parts and how quickly this misfire developed. I have hard time believing that it would make a difference. The truck was running excellent before this issue.

I attached photos of the cap and rotor hopefully it helps.

Sorry for the long post but thank you for your help

 

P0300 is almost always caused by a fault in the secondary ignition: plug, wires, cap, rotor, ignition coil. Low fuel pressure can also cause it to set.

I'd start out with an AC Delco cap & rotor, (A year on an aftermarket cap is pretty good). Put a dab of silicone dielectric grease on each terminal of the cap, inside and out. In the image of the cap, the grease was not applied when the cap was replaced.

Next, most of the auto parts stores in your area, (Autozone, Advance, Thirlby, O'Reilly) rent/sell fuel pressure testers, get one! Key ON, engine OFF, fuel pump running, pressure must be 60psi to 66psi. It must remain above 55psi for at least 10 minutes after the pump shuts off. If it fails either part of this test, further testing is necessary to pinpoint the problem. Post your results.

 

Okay Captain I am convinced as soon as I slapped on the AC Delco cap and rotor my blazer ran perfect.

It just had me baffled how sudden it happened though within an hour it went from running perfect to running on 3 cylinders

Of course I had to be a fool though and I put a new ignition coil on it before I replaced the cap and rotor at least I replaced the original and have a back-up now

 

Here's another vote for AC Delco cap and rotor. I replaced the fuel pump in my wife's 2000 Blazer and it wouldn't start afterward. The fuel pressure was perfect and I had spark on the #1 plug. Compression was good. I replaced the wires with the Autolite Premium and the cap and rotor with AC Delco and used silicone dielectric grease on the cap terminals. The truck fired right up with just the slightest touch of the key and has run perfectly ever since. The parts guys look at me like I'm crazy for demanding AC Delco but it's worth every penny.

 

Two great testimonials! More people need to use AC Delco caps.... using is believing.

Blue00, did you put silicone dielectric on the terminals? Also, if you haven't checked fuel pressure and leakdown, might not be a bad idea. If nothing else, just as a benchmark for future reference.

BTW, are you in TC proper, or in the "Burbs"? I think I know where you were talking about, "speedway station then went across the street to buffalo wild wings"... US31 and S Airport, correct?

 

Yes, I made sure to get the dielectric grease on the terminals. I don't want to replace these parts any sooner than I have to.

I do need to check the fuel pressure again because I know its only a matter of time before the pump goes. I had to replace the pump when I bought the truck but I couldn't afford AC Delco after just buying the truck so I bought a cheap-o one off eBay.

That is the speedway I filled up at, its not where I usually fill up but I wasn't going to make it to my regular Mobil gas station. I am about 15ish miles out of TC proper.